The present invention relates, in general, to an ejector assembly for an injection molding machine, and to an injection molding machine equipped with such an ejector assembly.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
An injection molding machine of a type involved here includes a mold mounting plate and an ejector plate which is movable relative to the mold mounting plate. Multi-component or multi-colored injection-molded articles can be produced in many ways. One process involves the so-called indexing plate method which involves a modification of the injection mold such that an additional indexing plate is placed between two basic mold halves of the injection molding machine. The indexing plate is rotatable about a center axis and can be moved axially in length direction of the machine. The indexing plate forms a central part of the cavity for making a preform which can be unchanged. After detachment from the fixed mold part, the indexing plate turns about a fixed angle, for example 120° or 180°, for placing the preform in a further cavity for molding on a further component. As the indexing plate undergoes an axial stroke before being turned, contrary to mold halves arranged on turntables, a placement of the preform in a cavity is now possible having a contour which changes on the side facing the moving mold mounting plate so as to permit the formation of back injections for example. After turning operation, the indexing plate is again moved back axially to the respective cavities.
German Offenlegungsschrift DE 101 45 461 A1 describes various examples of injection molding machines with an indexing plate. One example involves the attachment of a rotary unit on the moving mold mounting plate. The rotary unit includes a housing for rotatable support of a gear. The gear is hollow on the inside and configured with several grooves. The rotatable shaft of the indexing plate is formed with a complementary multi-grooved profile and extends through the gear. The rotatable shaft has a mold-side end, which is connected to the indexing plate, and an opposite end, which is connected to a linear drive, e.g. a hydraulic cylinder, so that the indexing plate can move in and out in relation to the fixed mold component. Disposed in the housing of the rotary unit at a right angle to the length axis of the machine is a toothed rod which is in engagement with the gear and is moved forward and backward by hydraulic cylinders. In this way, the gear can be rotated by an angle in correspondence to the stroke of the toothed rod, i.e. always alternating between clockwise and counterclockwise.
Another example described in German Offenlegungsschrift DE 101 45 461 A1 involves the use of a hydraulic motor or electric motor for rotating the indexing plate. The motor is hereby received in a recess of the moving mold mounting plate and includes a hollow shaft with a multi-grooved profile in correspondence to the multi-grooved profile of the rotatable shaft of the indexing plate.
In order to accommodate a flow of fluids on the indexing plate of an injection molding machine, the rotatable shaft is formed with passageways, normally axial bores, which extend parallel to an axis of symmetry of the rotatable shaft substantially along the entire length thereof. These channels can then be used in the area of the indexing plate for passage of heating means, compressed air, electric supply lines, or the like. Supply of fluids is normally realized using so-called rotary feedthroughs which supply fluid regardless of the angular position of the rotatable shaft relative thereto. The rotary feedthrough is normally connected to the rotatable shaft in axially fixed but rotatable relationship. When undergoing an axial stroke before the indexing plate is turned, the rotary feedthrough moves axially jointly with the rotatable shaft and the indexing plate. Also, a replacement of indexing plates is labor-intensive because the rotatable shaft of a replaced indexing plate must be provided again with a rotary feedthrough, securely anchored thereto.
It would therefore be desirable and advantageous to provide an improved machine-side ejector assembly which obviates prior art shortcomings and which is simple and compact in structure to allow standard injection molding machines to be retrofitted therewith and their use with indexing plate feature, and easy exchange of various injection molding machines, while still being easy to maintain and reliable in operation.
It would also be desirable and advantageous to provide an improved injection molding machine which uses standard mold mounting plates while being applicable in a simple manner for operation with indexing plate (multi-component or multi-colored injection molding) and operation without indexing plate.